1. Field of the Invention
The present invention relates to an anaesthesia apparatus and to a method for operating an anaesthesia apparatus. In particular the invention relates to an anaesthesia apparatus comprising a reflector filter for reflecting anaesthetic agent exhaled from the patient.
2. Description of the Prior Art
Anaesthesia apparatuses are known in the art for providing anaesthetics to patients. The term “anaesthesia apparatus” as used herein encompasses also sedation apparatuses, which are a simpler form of anaesthesia apparatus.
Anaesthesia apparatuses typically have inspiration and expiration lines for providing and withdrawing breathing gas from the patient and a vaporizer for providing anesthetic into the breathing gas flow. The vaporizer can be placed in the inspiration line or in a branch connected with the inspiration line, to provide vaporized anaesthetic to the breathing gas flow. The inspiration and expiration lines are interconnected near the patient in a so called Y piece, which is in turn used to connect the apparatus to the patient.
Anaesthesia apparatuses are usually provided with a manual ventilation system in parallel with an automatic mechanical ventilation system and a ventilation selection switch for selecting between the manual and the mechanical ventilation system. The manual ventilation system typically includes a manual ventilation bag that can be squeezed by medical personnel to provide air to the patient and be allowed to expand during exhalation.
The anaesthetic agent is typically added in a suitable dose to the breathing gas close to the patient, so that the patient inhales a suitable amount of anaesthetic. Not all the anaesthetic agent will be consumed by the patient. The part that is not consumed is exhaled during expiration. Some anaesthesia apparatuses, such as the apparatus de-scribed in U.S. Pat. No. 5,471,979, also have a reflector filter for anaesthetic. The filter adsorbs anaesthetic that is not consumed by the patient and during inhalation re-leases it again so that it is provided to the patient instead of being expired together with the expiration gas. Such filters enable more efficient use of anaesthetics.
U.S. Pat. No. 6,152,133 discloses an anaesthetic delivery system in which a reflector filter as discussed above is used. A supply of flushing gas is provided, to flush retained an-aesthetic from the filter while the system is connected to a patient, without passing the flushing gas to the patient. In this way the amount of anaesthetic retained in the filter from the expired gas can be varied on demand.
Between patients pre-use check must be performed. This is traditionally done manually according to recommended procedures such as the FDI “Anesthesia Apparatus Checkout Recommendations”. Today this is typically done in a combination of manual and automatic steps, by running a self test program which for example re-quires occlusion of the Y piece at certain stages in the program. In the prior art this is done manually. Hence, the pre-use check requires the attention of an operator who must be available such as for occluding the Y piece when required by the self test program.
Also, between patients the system must be flushed, to ensure that there is no anaesthetic left in any of the filters or other units in the apparatus. This is particularly important if another anaesthetic agent is used for the next patient.
In conventional anaesthetic apparatuses it is sufficient to flush out the gas that is pre-sent in the breathing circuit of the system to ensure that all anaesthetics has been removed. In systems using a reflector filter, such as the ones disclosed in U.S. Pat. Nos. 5,471,979 and 6,152,133, the amount of anaestetic agent retained in the reflector is much higher compared to the amount contained in the gas volume of the tubing. Thus, it is necessary to ensure that all of the anaesthetic agent that is present in the reflector filter is also flushed out before the apparatus is used again. Alternatively the whole filter must be replaced by a new filter, which is expensive and cumber-some. The cited documents do not propose any solution to this problem.